The need for small, fast, and sensitive detectors of biological agents which are able to continuously monitor an environment for extended periods of time is underscored by the proliferation of biological and chemical weapons, the poor man's nuclear weapon. Under battlefield conditions, a useful detector would rapidly alert a soldier when a specific biological or chemical agent is detected so that countermeasures can quickly be implemented.
Such detectors would be useful in non-military applications as well. Rapid detection of antibiotic-resistant bacteria in a patient would help clinicians select a more effective therapeutic regimen. Continuous monitoring of a city's drinking water supply would provide early warning of potential pathogens, giving public works officials more time to manage the potential health risks to the public. In addition, the use of these detectors in meat and poultry inspections would be a significant improvement over the current "poke-and-smell" procedure.
All vertebrates acquire a specific immune response to a foreign agent (antigen) in part by generating an immense diversity of antibody molecules. Antibody molecules bind to antigen with high specificity, e.g., they can differentially bind to two closely related strains of bacteria or viruses.
Antibodies are produced by B cells, a crucial component of the immune system. An antigen can activate a B cell by binding to antibodies on its surface, leading to a cascade of intracellular biochemical reactions which causes a calcium ion influx into the cytosol of the B cell.
For a review of antibody structure and function and B cell activation, see Paul, editor, Fundamental Immunology, 3rd ed., Raven Press, New York (1993).